Microwave Ablation of Primary and Secondary Lung Malignancies: A Phase I-II Single Centre Prospective Safety and Efficacy Trial

Surgery is the first choice of treatment for early-stage primary pulmonary malignancies, but up to 15% of all patients, and 33% of patients greater than 75 years of age, are not surgical candidate's due to locally advanced disease, poor cardiopulmonary reserve and significant medical co-morbidities. Some patients are also unwilling to undergo surgery. This has prompted the development of alternatives to surgery so that local control of unresectable tumors can be achieved.

Stereotactic body radiation therapy (SBRT) is currently an alternative therapy for these patients with 3-year survival rates of between 42 and 60%. SBRT has excellent local control rates and a favorable toxicity profile relative to other surgical and non-surgical therapies. Radiation pneumonitis (RP), amongst others, is one of the major toxicities which can limit the maximal radiation dose that can be safely delivered to thoracic tumors. Reported rates of SBRT induced RP requiring clinical intervention range from 0% to 29% and life-threatening toxicities have been reported in up to 12% of cases in various studies. The potential for toxicities from SBRT could limit the number of times a patient could be treated with SBRT for residual, recurrent or new pulmonary lesions over time.

Following the first report of thermal ablation for lung malignancies in 2000, this modality has been used to treat primary and secondary malignancies and has emerged as an effective, low-cost, safe and repeatable alternative to SBRT for local tumour control. The most widely practised technique is radiofrequency ablation (RFA). Microwave ablation (MWA) is a relatively new therapy and offers all the advantages of RFA, but with significant additional advantages 3. These include reduced procedure times, lower complication rates, increased ablative temperatures, improved propagation of thermal energy particularly in the lung, improved efficacy in lesions that are in close proximity to blood vessels due to reduced heat-sink effect, and less procedure associated pain 2,3. Using high energy MWA to treat 87 pulmonary tumors, Egashira et al achieved a primary technical success rate of 94% and technique effectiveness of 98% at a median of 15 months.

MWA is performed by Interventional Radiologists using CT guidance. The treatment is performed under general anaesthesia and is repeatable. Multiple lesions can be ablated in one treatment session. Patients can potentially be discharged the same day of treatment, if there are no adverse events.

MWA is a relatively new treatment option that could be considered in situations where the patient is not a candidate for further treatment with surgery, SBRT or chemotherapy, or the patient declines the recommended standard available treatments.

Objectives for Phase I:

The primary objective for Phase I of this study will be to demonstrate the Safety of MWA performed for treatment of lung malignancy in patients not suitable for surgery, chemotherapy or SBRT.

Primary objective (Safety): to determine the proportion of patients experiencing local adverse events at one week definitively related to the mwa procedure.

Secondary objective (Feasibility): To determine the proportion of patients in whom technical success of MWA was achieved by assessing completion of ablation on CT at the time of the procedure, indicated by replacement of tumor by ground glass change (including a 5mm ablation zone in normal surrounding lung parenchyma).

Objectives for Phase II Primary objective (Efficacy): To demonstrate efficacy by measuring the proportion of patients demonstrating absence of residual tumor on follow up CT at 1 month after MWA.

Secondary objective: To determine the proportion of patients needing re-treatment for recurrent tumor at 1 month post MWA.